Method for producing a one piece multifocal lens blank and lens



l -Dec v F. E. DL'JCKWALL 2,306,868

METHOD FOR PRODUCING A ONE PIECE MULTIFOCAL LENS BLANK AND LENS FiledMay 25. 1940 Patented Dec. 29, 1942 METHD FOR PRODUCING A ONE PIECEMULTE'CAL LENS BLANK AND LENS Application May 23, 1940, Serial No.336,748

S Claims.

This invention relates to a method for effecting an operation in theproduction of a one-piece multiiocal lens blank and lens having anoncircular inner near vision eld.

In the production of such lenses, it is customary to first surface ablank with a circular inner near vision field usually having its centersubstantially at the normal center or axis of the blank, and with agreater radius of curvature. The vaxis of the blank, as herein referredto, is the line passing through the centers of curvature of the innerand outer fields.

it has been proposed in providing a non-circular inner field, asdistinguished from one-piece biiocal lenses of the Ultex type, to grindaway or remove a portion of the inner field so that it becomes a part ofthe outer field, by means of a cam which guides the path of movement ofthe grinding and polishing buttons to conform with the desirednon-circular curvature. This is disclosed in Letters Patent to Taylor,No. 2,097,001, issued October 26, 1937; Letters Patent to Houchin No.2,087,687, issued July 20, 1937; and4 Letters Patent to Hubbell No.1,928,538, issued September 26, i933. producing such a blank and lens,to first grind and polish a circular inner eld slightly depressed withrespect to the outer eld. Following this method, the outer eld isultimately polished down to merge with the depressed inner field.

It is found to be diicult in the commercial production of such blanks toeffect a grinding and polishing operation which will completely remove aportion of the inner field and at the same time cause the outer field tosmoothly merge with the remaining portion of the inner eld along thecircular portion oi the boundary line. Thus, when the ground portion ofthe inner eld has been polished so that it merges indistinguishably intothe adjacent portion of the outer field, the remaining portion of theouter field may, during this operation, be polished down below theadjacent surface of the inner field along the circular boundary line,which would leave an undesirable shoulder. On the other hand, if theouter eld were polished down just suflicient to cause a smooth mergingor the surfaces along the circular portion of the boundary line, theground away portion of the inner field may not have been sufficientlypolished down to indistinguishably merge with the adjacent portion ofthe outer field.

The purpose of this invention is to provide a method which Will give alittle more leeway or permit of greater tolerance in the polishing op-However, it is desirable in eration, whereby the inner and outer fieldsare so related that the ground away portion of the inner eld will be ofthe'same surface curvature and of surface continuity with the adjacentsurface of the outer field, while there will still remain a slightdepression of the remaining portion of the inner field with respect tothe outer field along the circular portion of their boundary line. Withthis condition, the polishing of the outer field may then be continuedwith emphasis being directed toward lowering its surface by polishingjust sufficiently to cause it to smoothly meet and merge with thesurface of the inner field along such remaining circular portion oftheir separating boundary line.

This is accomplished by grinding and polishing the original circularinner iield slightly eccen tric with respect to the axis of the blank sothat the portion which is to be ground away is less depressed relativeto the outer field than the portion which will be bounded by thecircular portion of the boundary line. Conversely, along the circularportion of the boundary line as it will appear in the finished blank,the inner field will be more deeply depressed and have a greatershoulder than that portion of the boundary line which will be ultimatelyremoved. This relative arrangement oi the two surfaces will then permitof shallcwer grinding and polishing adjacent the removed inner fieldthan will be required throughout the remaining surface of the outerfield, for the purpose of allowing the two successive polishingoperations above referred to.

The full nature of the invention will be understood from theaccompanying drawing and the following description and claims:

Fig. 1 is a plan view of a lens blank showing the relative position ofthe ground and finished inner near vision eld with respect to the axisof theblank. Fig. 2 is a sectional view of the blank holder mounted onthe spindle for rotation upon an axis oiset from the axis of the blank,with the polishing button applied thereto. Fig. 3 is an enlarged planview of the inner eld indicating the position of the grinding orpolishing button relative to the axis of the blank. Fig. 4 is a sectionon the line ri-fl of Fig. 3, showing the depth of the inner held greatlyexaggerated. Fig. 5 is an enlarged and exaggerated sectional view of aportion of the blank showing a cam button secured to the inner field forcontrolling the grinding and polishing operation of the outer fled- Fig.6 is an enlarged and exaggerated section of the blank with the cambutton removed and indicating those surface portions of the blank to beground and polished away to provide the finished outer field. Fig. 7 isthe same as Fig. 6 showing the finished blank. Fig. 8 is a plan View ofthe finished lens.

Reference may be made to Letters Patent to Taylor No. 2,097,001, issuedOctober 26, 1937, and particularly Figs. 1 to 4 and 9, as disclosing onemethod of producing a multifocal lens blank and lens.

A blank is first ground in the usual manner, and on the usual spindle,with its axis X concentric with aXis of rotationV of the spindle. isaccomplished substantially in the manner illustrated in Fig. 2 with theeccentric extension l removed, and resulting ina blank I0 as shown inFig. 1 having an inner near vision field ii indicated by dotted lines.

Thereupon said blank is further ground with its inner field I Ieccentric of the axis. X, with its center positioned at Y, andsurrounded by the outer distance vision field I2, as is illustrated infull lines in Fig. l. As shown in Fig. 2, this is accomplished bymounting the blank on the holder I3 in the usual manner, to be driven bythe usual driving spindle I4, as is customary in the art.

For the purpose of this invention, the spindle I4, after the preliminarygrinding, is provided with an eccentric extension I5 interposed betweenthe spindle and the holder. Thus, the axial center of the holder and thespindle I-i' extends through the axis X of the blank. But by reason ofthe eccentric extension I5, the axis of rotation thereof, together withthe hold-er and blank, will extend along the dotted line Y. Uponapplying a grinding or polishing button i6 in the usual` manner, theinner field- Ii, upon rotation of the blank, will be reformed orenlarged with its center Y slightly offset from the axis of the blank asindicated at X and illustrated in Figs. 3 and 4.

As shown in Fig. 5, a cam button l'! is secured by cementing orotherwise, over a portion of the inner eld in the manner more fully setforth and described in said above-mentioned letters patent. This is forthe purpose of guiding the grinding and finishing operation on the outerfield during which a portion of the inner field ll is removed, leaving anon-circular inner field in the finished blank and lens.

By reason of the eccentric or off-center grinding of the inner eld,as'illustrated and greatly exaggerated in Fig. 6, the slightly depressedinner field is surrounded by a circular shoulder boundary line i3 whichis of greater dep-th at the side distant from the axis X of the blank,as indicated at A than at the near side, as indicated at B. The purposeof grinding or finishing the inner field eccentricaliy, is to obtainthis variation in depth of its depression for allowing more tolerance inthe grinding and polishing of the outer eld for the reasons abovediscussed.

The next operation in producing the finished lens is to grind down thatportion It! of the inner field which is exposed by the cam button l?, asshown in Fig. 5, until it takes the curvature of the outer eld andbecomes substantially a continuation of the outer field surface I2.Thereupon, the whole of the outer field i2, together with said portioni9 of the inner field, is polished until the heaviei` shadedl portion,indicated by C in Fig. 6, is removed, which completely eliminatestheshoulder indicated atB, while the.

This

reduced shoulder indicated at A remains. This is due to the eccentricrelation of the inner field resulting in the shoulder B being of lessdepth than the shoulder A. The final step resides in the furtherpolishing of the entire outer iield, removing that portion indicated atD resulting in the elimination of the remaining shoulder A. This latterstep is designed to bring the surface of the non-circular inner fieldinto smooth merging relation with the finished outer surface I2a aboutthe circular portion of its boundary line, as indicated at i8, butleaving a flat shouldered upper boundary line 2d.

In view of the above, it may be considered that there are threeoperations in the grinding and polishing of the blank after theeccentric inner field l has been formed. The first operation is thegrinding away of the exposed portion I9 of the inner field. The secondoperation is the polishing of the outer field until the ground awayportion it merges therewith, eliminating the shoulder B. This leaves theinner field slightly depressed with a minute shoulder A about theremaining circular boundary line thereof. The third operation consistsin polishing away the shoulder A left by this depression to eiect thesmooth merger of the finished fields II and I2a along this boundary lineI8, as illustrated in Fig. 7.

The invention claimed is:

l. The method of producing a one-piece multifocal vlens blank and lensconsisting in mounting a concave blank upon a holder, rotating saidholder and blank about an axis offset from the axis of the blank,applying a grinding and polishing tool to the concave surface of theblank adjacent and to one side of its axis of rotation, said grindingand polishing tool being formed to grind an inner near vision field withits center offset from the axis of said blank, whereby said field willbe ground eccentrically of said axis to provide a greater depth ofdepression about the side farther from said axis than about the otherside thereof, grinding and polishing away a portion of said inner fieldof lesser depth to the same curvature as the outer field, and polishingthe outer field to smoothly merge with the inner field about the curvedboundary line of its remaining portion.

. ishing tool to the concave surface of the blank adjacent and to oneside of its axis of rotation, said grinding and polishing tool beingarranged to grind an inner near vision eld with its center lying to oneside of the axis of said blank whereby said field will be groundeccentrically to provide a greater depth of depression about the sidefarther from said axis than about the other side thereof, grinding awaythe portion of the inner field which is of lesser depth to substantiallythe same surface curvature as the outer iield,

polishing the outer field to effect surface continuity between it andthe ground away portion, and continuing the polishing of the outer fielduntil it smoothly merges with the remaining portion of the inner fieldabout the curved portion 0f its boundary line,

3. The method of producing a one-piece multifocal lens blank and lensconsisting in grinding and polishing a depressed circular inner nearvisionA field Within an outerdistanoe vision field and eccentrically ofthe axis thereof to provide said inner field with a depth of depressionrelative to said outer field greater on one side than the other,grinding and polishing away a portion of the said inner field on theside thereof having lesser depth to the same curvature as the outerfield while leaving a surface elevation about the remaining portionthereof, and polishing the outer field to smoothly merge with saidremaining portion of the inner field about the curved boundary linetherebetween.

4. The method of producing a one-piece multifocal lens blank and lensconsisting in forming a depressed inner field having a circular boundaryline separating it from the outer field, grinding and polishing saidinner field so that the depth of the depression about said boundary linewill be greater on one side thereof than on the other, grinding andpolishing the surface of the outer field and the portion of the innerfield of lesser depth until said portion of the inner field is of thesame surface curvature as the outer field while leaving a surfaceelevation and shoulder of said outer field about the remaining portionof the inner field due to said difference in depth, and thereafterpolishing the outer field to reduce said remaining surface elevationuntil it smoothly merges with the remaining portion of the inner fieldalong the remaining curved boundary line therebetween.

5. The method of producing a one-piece multifocal lens blank and lensconsisting in grinding and polishing a circular inner near Vision fieldslightly depressed within an outer distance vision field, grinding andpolishing said inner field with respect to the outer field to produce adepth of depression greater on one side than the other, grinding away a.portion of the lesser depressed inner field to substantially the samesurface curvature as the adjacent portion of the outer field, polishingthe outer field to effect substantial surface continuity between it andsaid ground away portion of the inner field while leaving a surfaceelevation and shoulder of said center field about the remaining portionof the inner field due to said difference in depth, and continuing thepolishing of the outer field surface until it smoothly merges with theremaining portion of the inner field along the curved portion of itsboundary line.

6. The method of producing a one-piece multifocal lens blank and lensconsisting in grinding and polishing a circular inner near vision fieldslightly depressed within an outer distance vision eld, grinding andpolishing said inner field L eccentrically of the axis of the blank toincreased area for providing a depth of depression greater on one sidethan the other, grinding and polishing away a portion of the lesserdepressed inner field to the same surface curvature as the adjacentportion of the outer field while leaving a shouldered elevation of theouter field in respect to the balance of the inner field due to greaterdepression thereof, and polishing the outer field to smoothly merge withthe remaining portion of the inner field about the curved boundary linetherebetween.

'i'. The method of producing a one-piece multifocal lens blank` and lensconsisting in grinding and polishing a circular inner near vision fieldslightly depressed within an outer distance vision field, grinding andpolishing said inner field slightly offcenter with respect to the axisof the blank to increased area for providing a depth of depressiongreater on one side than the other, grinding away a portion of thelesser depressed inner field to the same surface curvature as theadjacent portion of the outer field, polishing the outer field to effecta continuity of surface between it and the ground awa;r portion Whileleaving a shouldered elevation of the outer field in respect to thebalance of the inner field due to greater depression thereof, andcontinuing the polishing of the outer field and said inner field portionuntil said outer field smoothly merges with the remaining portion of theinner field along the curved portion of its boundary line.

8. The method of producing a one-piece multifocal lens blank and lensconsisting in mounting a concave blank upon a grinding and polishinghead, rotating said head about an axis displaced from the axis of saidblank, applying a grinding and polishing tool t0 the concave surface ofthe blank while rotating about its displaced axis to form a depressedinner near vision field with the center of said field offset from saidaxis whereby the depth of depression on one side of said field will begreater than on the other, grinding off a portion of the inner field onthe side of less depth to the same surface curvature and continuity asthe surrounding field of the blank while leaving a shouldered elevationof the outer field in respect to the balance of the inner field due togreater depression thereof, and polishing the surrounding fieldincluding said portion to smoothly merge with said balance of the innerfield along the curved boundary line therebetween.

FRANK E. DUCKWALL.

